Bats for hitting balls vary with the particular game being played, but they have the common characteristic of comprising a handle portion at one end for grasping the bat, and a barrel portion at the other end for hitting the ball and an intermediate portion connecting the two end portions. In the case of the American baseball, for example, there are differences between bats used for professional baseball, bats used for the soft ball, and bats used for Little League games, but in general a design good for one of these uses can be adapted to the other uses.
Wooden ball bats have been conventional for years in all three types of American baseball mentioned above. However, the combination of population increase and lumber resources decrease has led to a search for other materials for making such bats. While all sorts of metals might be used, aluminum and aluminum base alloys are especially well suited for this purpose, considering strength to weight ratio, surface chracteristics, formability and cost. While aluminum bats presently cost more than wood bats, they have the great advantage of lasting longer, and hence of costing less in the long run.
Early efforts to develop aluminum bats included the approach of mounting a cylindrical tube of extruded aluminum in a lathe and spinning it down by pressure of a blunt instrument against the outside of the workpiece as it was rotated with a shaping mandrel inside. The resultant shaped metal bat stock had its original extruded form along one end, where it was designed to hit balls, an intermediate tapered portion and a reduced diameter at its handle end, where it was designed to be gripped. A bat made in this way had generally uniform thickness of its metal wall from end to the other. The metal at the tapered portion and the handle end was forced longitudinally away from the center of the bat, thus lengthening the original cylindrical extrusion. There was less metal per unit length at the tapered and handle end of the bat, because of the uniformity of wall thicknes in conjunction with decreased diameter at the tapered and handle end. As a result, the center of gravity of the bat was displaced from the geometric center of the length of the bat in the direction of the hitting end of the bat. A bat made in this way thus had its weight per unit length concentrated toward the hitting end, where it should be for best results, and where it exists inherently in conventional solid wooden bats. Unfortunately, the spinning step was relatively expensive, and this system of bat manufacture apparently has never been employed on a large commercial scale.
An improvement over the turned bats is disclosed in Swenck's U. S. Pat. No. 3,691,625 issued Sept. 19, 1972. In accordance with the teaching of that patent, a length of cylindrical aluminum extrusion is swaged down in a rotating die having a tapered throat into which one end of the extrusion is pressed. As the the die rotates, the metal is compressed. As compression occurs, the metal extrusion is thrust further into the die, until the workpiece has completed a predetermined distance of movement into the die. As explained in the patent, the swaged down portion of the workpiece is then internally drilled coaxially until at least most of the thickened end of the workpiece has been drilled out to leave a metal wall for the handle portion having a thickness not substantially greater than the wall thickness of the ball hitting portion of the bat.